This invention relates generally to keying systems and, more particularly, to keys for use with capacitive and ultrasonic keys and key sensors and to such keys and key sensors in combination with electronic circuitry for controlling locking mechanisms.
Keying systems for electrically controlling locking mechanisms have been known for decades. An example of an early such system is U.S. Pat. No. 2,008,150, issued July 16, 1935 to A. S. Nelson in which a light source is interrupted by movable elements to control the source's light rays received at a light sensor which in turn controls a bolt. The Nelson patent references patents on electromagnetically operated locks as early as 1876.
More modern electrical lock keying systems are disclosed in the following U.S. Pat. Nos.: 2,692,495, Verdan, Oct. 26, 1954; 3,231,693, McLaughlin, Jan. 25, 1966; 3,660,831, Nicola et al., May 2, 1972; 3,705,277, Sedley, Dec. 5, 1972; All of the above U.S. patents are incorporated herewith by reference. In the Verdan, McLaughlin and Sedley patents, respectively, counter keys, set cards and program cards are housed in the locking mechanism and correspondence with a "key" is required to unlock the mechanism. Various means are disclosed or suggested to encode the "keys" and corresponding "counter keys" in the lock housings including magnetic, mechanical, electrical, electro-mechanical, electro-optic, pneumatic and hydraulic type devices. Nicola et al describes a system having an electronic logic circuit to sense electrical contacts established by a key. Hall effect sensors are also known in the prior art.
One disadvantage of key/counter-key systems is the requirement for individually inserting and replacing the counter keys at each lock in order to change the lock coding. Also, the various prior art sensing arrangements all suffer from one or more disadvantages such as susceptibility to key or sensor wear by way of the wearing of moving parts or the degradation of contacts between the key and sensor, key complexity and expense, sensor complexity and expense and susceptibility to dirt.